56 research outputs found
Quantum computation with the Jaynes-Cummings model
In this paper, we propose a method for building a two-qubit gate with the
Jaynes-Cummings model (JCM). In our scheme, we construct a qubit from a pair of
optical paths where a photon is running. Generating Knill, Laflamme and
Milburn's nonlinear sign-shift gate by the JCM, we construct the conditional
sign-flip gate, which works with small error probability in principle. We also
discuss two experimental setups for realizing our scheme. In the first
experimental setup, we make use of coherent lights to examine whether or not
our scheme works. In the second experimental setup, an optical loop circuit
made out of the polarizing beam splitter and the Pockels cell takes an
important role in the cavity.Comment: 4 pages, 2 eps figures, latex2e; v2: Figure 1 and its caption are
modified; v3: one new section is added; v4: experimental setups are
completely rewritten; v5: minor corrections; v6: two references added; v7: 18
peges, 11 eps figures, PTPTeX, LaTeX2e, Section 4 is rewritte
Interaction-free measurement with an imperfect absorber
In this paper, we consider interaction-free measurement (IFM) with imperfect
interaction. In the IFM proposed by Kwiat et al., we assume that interaction
between an absorbing object and a probe photon is imperfect, so that the photon
is absorbed with probability 1-\eta (0\leq\eta\leq 1) and it passes by the
object without being absorbed with probability \eta when it approaches close to
the object. We derive the success probability P that we can find the object
without the photon absorbed under the imperfect interaction as a power series
in 1/N, and show the following result: Even if the interaction between the
object and the photon is imperfect, we can let the success probability P of the
IFM get close to unity arbitrarily by making the reflectivity of the beam
splitter larger and increasing the number of the beam splitters. Moreover, we
obtain an approximating equation of P for large N from the derived power series
in 1/N.Comment: 6 pages, 3 eps figures, latex2e; v2: minor corrections; v3: the title
is change
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